1. Field of the Invention
The present invention relates to a photographing apparatus. More particularly, the present invention relates to a photographing apparatus for minimizing the effect of shaking on an image.
2. Description of the Related Art
Photographing apparatuses, such as still cameras and video cameras, include an image pickup device and convert light emitted to the image pickup device into an image signal.
The photographing apparatuses may include an image shake correction device to prevent shake of an image. The image shake correction device detects vibrations applied to the photographing apparatus and moves the image pickup device according to the detection result to prevent shake of an image formed on the image pickup device.
Generally, the image shake correction device makes the image pickup device move along an X-axis and a Y-axis, which perpendicularly intersect each other, according to the movement of the photographing apparatus.
An image shake correction device embedded in a photographing apparatus is disclosed in Japanese Patent Application No. 2006-128621 by the inventor of the present invention.
FIG. 1 is a plan view of a conventional image shake correction device 10. FIG. 2 is a cross-sectional view taken along line I-I in FIG. 1.
Referring to FIG. 1, a photographing apparatus includes a charge coupled device (CCD) image sensor 12, and the conventional image shake correction device 10 includes a base plate 80 fixed to a main body of the photographing apparatus, a slider 20 installed on the base plate 80, and a CCD base 90 installed on the slider 20 having the CCD image sensor 12 to be mounted thereon.
The slider 20 and the CCD base 90 constitute an image pickup device stage. The slider 20 can move in an X direction with respect to the base plate 80, and the CCD base 90 can move in a Y direction with respect to the slider 20.
Piezoelectric actuators 40 and 42, disposed in a driving force generating portion, include piezoelectric elements. When active portions, which are formed at front ends of the piezoelectric actuators 40 and 42, elliptically move, the image pickup device stage contacting the active portions moves.
The piezoelectric actuator 40 and a support portion 56 are fixedly installed on the base plate 80, the active portion is formed at the front end of the piezoelectric actuator 40 contacts a protrusion 32 protruding from the slider 20, and a ball bearing 36 is inserted between the protrusion 32 and the support portion 56.
A ball holder 60 is fixedly installed on the base plate 80, and a long-hole groove 62 (see FIG. 2) is formed in the ball holder 60 along a virtual straight line P extending from the protrusion 32.
A long-hole groove 22 is formed in a surface of the slider 20 facing the long-hole groove 62, and a ball bearing 64 is arranged between the two long-hole grooves 62 and 22. The long-hole grooves 62 and 22 and the ball bearing 64 constitute a guide portion. Accordingly, the slider 20 can move along the straight line P due to the driving force of the piezoelectric actuator 40.
The piezoelectric actuator 42 and a support portion 92 are fixedly installed on the CCD base 90, the active portion is formed at the front end of the piezoelectric actuator 42 contacts a protrusion 34 of the slider 20, and a ball bearing 38 is inserted between the protrusion 34 and the support portion 92.
A long-hole groove (not shown) is formed in the CCD base 90 along a virtual straight line Q extending from the protrusion 34. A long-hole groove 24 is formed in a surface of the slider 20 facing the long-hole groove of the CCD base 90, and a ball bearing 96 is arranged between the two long-hole grooves. The two long-hole grooves and the ball bearing 96 constitute a guide portion. Accordingly, the CCD base 90 can move along the straight line Q due to the driving force of the piezoelectric actuator 42.
A ball bearing 91 is inserted into a bearing groove 26 and disposed between the CCD base 90 and the slider 20. A ball bearing 84 is inserted into a bearing groove 97 and disposed between the slider 20 and the base plate 80.
A ball bearing 93 is inserted into a bearing groove 28 and disposed between the CCD base 90 and the slider 20. A ball bearing 86 is inserted into a bearing groove 98 and disposed between the slider 20 and the base plate 80. The CCD base 90 is attracted to the base plate 80 by a magnet 52.
According to the conventional image shake correction device 10, either the straight line P connecting an operating portion of the piezoelectric actuator 40 and the guide portion, or the straight line Q connecting an operating portion of the piezoelectric actuator 42 and the guide portion, passes over the CCD image sensor 12. As a result, since a distance between the center of the CCD image sensor 12 and the operating portions of the piezoelectric actuators 40 and 42 is shortened, the conventional image shake correction device 10 can reduce a moment caused by the CCD image sensor 12, thereby more efficiently following vibrations caused by hand shake.
However, as described hereinafter with reference to FIGS. 2 and 3, the photographing apparatus including the conventional image shake correction device 10 may fail to capture an image in which image shake is prevented with high precision.
FIGS. 3 and 6 are plan views of the conventional image shake correction device 10. FIG. 4 is a cross-sectional view taken along line II-II of FIG. 3. FIGS. 5 and 7 are enlarged plan views of parts of the conventional image shake correction device 10.
Referring to FIG. 3, if the slider 20 moves in a negative direction of an X-axis, the ball bearing 36 rolls in the negative direction of the X-axis, and thus an operation point of the driving force of the piezoelectric actuator 40 and a position of the ball bearing 36 do not match each other. In this case, pressure from the piezoelectric actuator 40 causes a rotating moment around the ball bearing 36 in an X-Y plane of the CCD image sensor 12.
Therefore, referring to FIG. 4, the long-hole groove 22 of the slider 20 contacts a side surface of the ball bearing 64, the pressure is further applied to the slider 20, and the slider 20 tends to climb on top of the ball bearing 64. As a result, either the slider 20 or the CCD base 90 moves along a Z-axis, which is perpendicular to the X and Y-axes, despite the magnet 52 attracting the CCD base 90 to the base plate 80.
For example, referring to FIGS. 5 and 7, each of widths of the long-hole grooves 62 and 22 along the Y-axis are slightly greater than a diameter of the ball bearing 64 so that the ball bearing 64 can rotate. Therefore, the slider 20 can move not only along the X-axis, but also along the Y-axis as much as a difference between each of the widths of the long-hole grooves 62 and 22 and the diameter of the ball bearing 64.
Accordingly, referring to FIGS. 4 and 5, when the slider 20 moves in the negative direction of the X-axis, the slider 20 also moves in a negative direction of the Y-axis with respect to the ball holder 60 according to position relations between the long-hole groove 22 of the slider 20, the long-hole groove 62 of the ball holder 60, and the ball bearing 64.
Also, referring to FIG. 6, if the slider 20 moves in a positive direction of the X-axis, the ball bearing 36 rolls in the positive direction of the X-axis, and thus the operation point of the driving force of the piezoelectric actuator 40 and the position of the ball bearing 36 do not match each other. In this case, pressure from the piezoelectric actuator 40 causes a rotating moment around the ball bearing 36 in the X-Y plane of the CCD image sensor 12. The rotating moment caused when the slider 20 moves in the positive direction of the X-axis is opposite in direction to the rotating moment caused when the slider 20 moves in the negative direction of the X-axis. Position relations between the long-hole groove 22 of the slider 20, the long-hole groove 62 of the ball holder 60, and the ball bearing 64 are shown in FIG. 7. That is, the slider 20 moves in a positive direction of the Y-axis with respect to the ball holder 60.
Comparing FIGS. 3 through 7, a position relation between the piezoelectric actuator 40 and the ball bearing 36 is reversed by the movement of the slider 20 along the X-axis, and a rotating moment around the ball bearing 36 is also reversed. As a result, the slider 20 moves either in the negative or positive direction of the Y-axis. Generally, the difference between each of the widths of the long-hole grooves 62 and 22 along the Y-axis and the diameter of the ball bearing 64 is greater than one pixel of the CCD image sensor 12 due to restrictions such as manufacturing precision. Accordingly, the conventional image shake correction device 10 cannot prevent image shake with high precision because of the movement of the slider 20 along the Y-axis.
For example, as shown in FIG. 3, if the slider 20 moves in the negative direction of the X-axis and the ball bearing 36 extremely moves in the negative direction of the X-axis, the ball bearing 36 deviates very much from the operation point of the piezoelectric actuator 40. In this case, the slider 20 is bent significantly due to the pressure from the piezoelectric actuator 40. As a result, a vibration mode caused by the bending may resonate with vibrations of the piezoelectric actuator.